A means of continuously monitoring the effluent from a gas chromatography column with a mass spectrometer and an oscilloscope is described. Any sixteen-mass-unit portion of a spectrum can be displayed and the smallest change in the pattern seen immediately. The scan rate can be altered so as to decrease the time required for the sixteen-mass-unit display, or to present a larger portion of the spectrum. The method can be adapted to the study of such events as pyrolysis, reaction rate, thermal cracking, etc. The presence of intermediate compounds formed during a reaction can be detected quickly. These are only a few of the many uses to which a commercially available mass spectrometer may be adapted by means of this easily made modification which make it a more valuable tool where investigations of volatile materials are being made.